Normally, engines, such as diesel engines which use fuel injection pumps for delivering fuel to the engine via fuel injectors and gasoline engines which may use either fuel injection pumps or carburetor fuel supply systems, normally include an adjusting screw which controls the amount of fuel delivered to the engine, particularly under idle or no-air engine operating conditions. It is conventional for this adjustment screw to be pre-set by the manufacturer of the vehicle or engine. To prevent tampering with this adjustment to increase horsepower, and resultant premature failure of engine components, it has also been common practice to block access to the adjusting screw by a cover plate or cover plug. To further discourage tampering, a tamper-resistant seal in the form of a sealing wire and metal tag seal, is often associated with such a cover or plug as well. However, the temptation to a driver of the ability to boost engine horsepower by tampering with the fuel adjustment screw is sufficiently great that neither the presence of a cover plate and/or tamper seal is sufficient, in an of itself, to deter resetting of the fuel adjustment screw.
Thus, various attempts have been made to render shielding of the adjustment screw of a fuel supply system more effectively tamper-proof. For example, Tateno U.S. Pat. No. 4,308,220 discloses a tamperproof protecting construction wherein a sealing plug is force-fit into a chamber defined by a tubular protective wall which projects axially above the adjusting screw. The protective plug is held securely within the tubular protective wall due to the fact that the plug has a cup-like shape, the perimetric wall of which, in its unstressed state, is slightly larger than the inner size of the tubular protective wall chamber into which it is wedged and because the only access to the plug for removal thereof is via a slot for a prying rod which is dimensioned not to accept standard tools of the type found in a garage of machine shop.
However, it is not unthinkable that a resourceful driver or mechanic would be able to find a suitable rod for use in prying out the protective plug and the circular cylindric shape of the plug and chamber also affords the possibility of punching through the protective plug and turning both the screw and plug jointly. More importantly, however, is the fact that when circumstances make it necessary or beneficial to locate the adjustment screw within a large recess that is shared with other components, use of a wedged-in plug may not be feasible or desirable, particularly if access to the component sharing the recess with the adjustment screw is necessary.
Byrnes, Jr. U.S. Pat. No. 4,273,730 shows a tamper-resistant idle adjustment screw arrangement whereby the noted problem of gaining the ability to reset an adjustment screw by pryiny out, or punching or drilling through a seal plug covering the adjustment screw is solved via the provision of a blocking pin between the plug and adjustment screw that may be removed from its blocking position only by removing the carburetor from the engine to which it is associated. However, the location of the adjustment screw may not always afford the ability to implement such a solution, nor will such a solution usually be available with respect to the adjustment screw of an engine fuel pump.
Another approach which has been taken for the purpose of denying unauthorized access to the fuel adjustment screw of fuel supply systems has been the mounting of a cover plate thereover by non-removable means. For example, U.S. Pat. No. 4,272,458 to Ruth et al discloses a tamper-resistant idle adjustment screw arrangement for a carburetor wherein a U-shaped cover is mounted over the idle adjustment screws and removal thereof is precluded by virtue of the fact that the cover is secured by a rivet, access to which cannot be obtained without first unmounting the carburetor from the engine. Besides the fact that such an arrangement normally will not be suitable in the environment and engine fuel pump, removal of the rivet proposes an obstacle to the making of an authorized adjustment to the adjustment screw, that is further complicated by having to remove the carburetor. Likewise, such an arrangement also may not be usable in the noted situation wherein the adjustment screw shares space within a large recess with another component to which access is necessary.
Owens U.S. Pat. No. 4,470,769 shows a tamperresistant seal for a fuel injection pump wherein access to the adjustment screw is blocked by a cover plate bracket that is fastened over the adjustment screw by one-way fastening screws and over which another cover is permanently attached by a locking device. Such a construction is relatively costly and shares the shortcoming of all of the noted prior art arrangements in that it too is unsuitable for use in the situation wherein the adjusting screw shares a common recess with a component with respect to which it is not possible or desirable to preclude access to.
Thus, there is a need for a tamper-proof adjustment screw arrangement by which access to an adjustment screw can be precluded, not only in a simple and effective manner, but under such circumstances wherein the adjustment screw is situated within a recess alaong with another component with respect to which continued access should be afforded.